This invention relates to fresh air make-up apparatus for a furnace or the like and more particularly to apparatus that provides preheated and diffused fresh air for both the building and the furnace combustion chamber.
In a conventional forced air heating system employing a fuel burning furnace, such as a gas fired furnace, fuel is burned in a combustion chamber of the furnace and the heat from the combustion gases is transferred in a heat exchanger to building air that is circulated through the building. A furnace blower receives the building air from a cold air duct and returns the heated air to the building environment through a warm air duct. Exhaust gases are exhausted through a flue to the atmosphere after they have warmed the room air in the heat exchanger.
The movement of heated combustion gases up the flue and out of the building is one factor that causes a negative pressure in a building. This condition causes gases to be replaced in the building principally by seepage through natural openings, such as gaps around windows, doors, or the like. In highly insulated and well sealed houses, however, replacement air through natural openings of the house may be substantially unavailable. This can cause a number of problems. The combustion chamber of the furnace may operate less efficiently if a substantial negative pressure condition persists. If the negative pressure condition becomes acute, exhaust gases may actually be dumped back into the building through the draft diverter or draft hood of the furnace. Such gases can be lethal.
In addition, if air is continuously recirculated in a house without an exchange of some fresh air, the air becomes stale and can pick up a number of unhealthy and sometimes toxic contaminants.
Various devices have been developed for providing fresh outside air to the combustion chamber of a furnace. Most such devices provide the fresh cold air directly to the combustion chamber, which is undesirable. Others have released the fresh air to the room where the furnace is located as a means for heating and diffusing the air, while still others have preheated the outside air with a heat exchanger connected to the exhaust flue.
Other types of devices have been developed for providing a fresh air exchange in a tightly closed building. In one system, fresh air is preheated by the exhaust flue and then discharged into the cold air return of the furnace.
It is one of the objects of the present invention to provide an improved fresh air make-up apparatus that provides fresh air to both the room environment and to the combustion area of the furnace, while filtering, diffusing, and preheating the air in a compact unit.